Like most things IT, testing something on the actual device you want to test for is the gold standard. It's probably the only way to be sure of picking up those little quirks that could spoil the look or functionality that you are after.
How often do you see a website where the colour scheme used is really bad? It can really detract from what can otherwise be a great site. Sure, 'content is king' but it doesn't hurt to try to get some of the design elements to work nicely together. On the other hand, I'm sure you will have seen a great looking site where the colours work comfortably together - maybe in such a way that you don't even consciously realise it.